The objective of this research program is to provide information on the functioning and maintenance of the vertebrate photoreceptor. Some of the reasons for studying this system are: (a) Vision is an important physiological system; (b) The receptor molecule, the visual pigment, rhodopsin is an intrinsic membrane protein with distinct conformational states; (c) The stimulus of the system - light - is a particularly controllable variable; and (d) Information on the functioning of the retina may provide insights into the functioning of the brain, since the retina is an embryological evagination from the brain. Because our interests in the vertebrate photoreceptor involve many objectives, a variety of approaches are used. In general they can be classified as biochemical, electrophysiological and genetic. At the rhodopsin level this involves spectrophotometric measurements of rhodopsin and its photoproducts, in detergent extracts or excised retinas. At the cellular level, this involves measurements of such parameters as oxygen consumption, ATP levels, protein phosphorylation and cyclic nucleotides. At the neurobiological level, this involves extracellular and intracellular electrophysiological measurements of the phototransduction, light adaptation and conductance processes of the cell. These techniques are applied to vertebrate preparations as well as to visually defective mutants of Drosphila (fruitflies).